The invention relates to a molded case ground fault trip unit capable of being coupled to a molded case of a breaking unit to form a ground fault current protective device. The breaking unit has, aligned on one of its faces, external terminals, and on the opposite face internal connection terminals to the ground fault trip unit. The terminals are connected two by two by conductors in which the breaking contacts of the breaking unit are inserted. The ground fault trip unit includes comprising a differential transformer through which several active conductors pass constituting the primary windings of the transformer, whose secondary winding electromechanically controls opening of the breaking contacts when a ground fault occurs.
A ground fault trip unit of the kind mentioned, associated with a breaking device, notably an electrical circuit breaker or switch, gives this device differential protection properties. The advantages of reduced manufacturing and storage costs of modular systems of this kind are well-known, and they are all the more considerable as the number of standard elements is limited.
The object of the invention is to provide a ground fault trip unit which can be used in different combinations with standard switches or circuit breakers to achieve three-pole or four-pole differential protection devices.